LAUSR

Abstract Stocking larger sized fish in fattening along with good aquaculture practices (GAP) are considered potentials for achieving sustainable and safe fish production under the climatically challenged drought-prone areas where the maintenance of optimal water level throughout the culture period is a real obstacle. To be sustainable, fattening requires optimal stocking density, as lower stocking density can bring up economic loss and at higher stocking density fish are severely challenged by stressors. The present study was designed to explore suitable stocking density for fattening of carp using overwintered fish and maintaining the aspects of good aquaculture practices. The present study was conducted for a period of 6 months from July to December 2019 in ponds of Rajshahi district, Bangladesh with three different treatments of carp stocking densities such as T1: 2470 fishes/ha; T2: 3705 fishes/ha and T3: 4940 fishes/ha. Individual stocking weight of all the fishes was kept significantly higher at T1, medium at T2 and lower at T3. However, stocking biomass was maintained significantly indifferent in all the treatments. Fishes were fed with pelleted feed (containing 25% crude protein, 10% moisture, 4–5% crude fat and 8% crude fiber) twice a day and water quality parameters were monitored monthly. Significant variation was observed only in dissolved oxygen, NH3-N, plankton cell density and total heterotrophic bacterial count. However, two opportunistic bacterial counts (Pseudomonas spp. and Aeromonas spp.) were higher at treatment T3, and the presence of non-indigenous pathogenic bacteria (Salmonella spp., Shigella spp. and Escherichia coli) was not evident in all the treatments. Significantly higher final weight and survival of fishes were obtained with treatment T1, while combined production of fishes was significantly higher at treatment T3 followed by T2 and T1. Furthermore, the higher market price of larger fishes at T1 resulted in significantly higher total return and benefit-cost ratio (BCR), in which the average selling price of fishes at T1, T2 and T3 were 250, 218 and 195 BDT/kg, respectively. The data obtained from this study has the potency to be used as baseline information on the sustainability of GAP based carp fattening in water deprived drought-prone areas in Bangladesh and other comparable geographical areas in the tropics.